1. Field of the Invention
The invention relates to an apparatus for continuously recording physiological data in ambulatory patients. More particularly, the invention teaches a physiological data recorder having a unique data compression means, an automatic calibration means, and a digital or analogue data playback means.
2. Description of the Contemporary and/or Prior Art
Gastroesophageal reflux disease (GERD) is a common clinical disorder in which esophageal irritation by regurgitated gastric contents produce symptoms and esophageal inflamation. Classical symptoms of heartburn and oral regurgitation of a sour or bitter liquid permit a reasonably reliable diagnosis without the need to resort to laboratory tests. However, GERD can occur with a large array of atypical symptoms that can mimic pulmonary, cardiac, biliary and non-esophageal peptic disease. With these atypical symptoms, laboratory evaluation for evidence of GERD is often necessary.
Unfortunately, currently applied clinical laboratory tests for the diagnosis of GERD are either too insensitive or too non-specific. For example, the traditional barium swallow study documents only about 40% of the refluxers while the acid perfusion test (the Bernstein test) is positive in as many as 10% of normal individuals and 40% of those with non-esophageal peptic disorders.
Over the past decade, continuous pH monitoring has been used to generate better information on GERD. A pH probe is placed via the nose into the esophageal lumen and the patient is allowed normal activity and ingestion of food. Intraesophageal pH is monitored through the recording period which usually ranges from 14 to 24 hours in duration. The aim is to provide a representative sample of both daytime and nighttime reflux activity under near physiologic conditions.
Many authorities consider the continuous pH monitor to be the best single test for the diagnosis of GERD. In addition, it provides valuable information on the pathogenesis of reflux and is the first test to provide meaningful information on the effect of therapy on the severity of reflux. However, prior art devices for continuously monitoring pH in ambulatory patients are inadequate.
Typical physiological data recorders which are useful with ambulatory patients fall into two general categories. The first category includes physiological data recorders which collect and record physiological data which are periodic in nature and have a recognizable waveform. Electrocardiagram recorders are typical of this category and look for irregularities in the EKG waveform before recording immediately proceeding or following signals. U.S. Pat. Nos. 3,755,783 and 4,250,888 are typical physiological recorders which analyze irregularities in repetitive biological processes.
The second category includes physiological data recorders which record a physiological phenomenon which is not a repetitive biological process. This category requires an extremely large data storage capacity since there is no simple function which allows normal performance to be distinguished from abnormal performance. Continuously recording intraesophageal pH falls into the second category. The episodic nature of the gastroesophageal reflux behavior is not a repetitive biological process with a clearly recognizable pattern.
Prior art physiological recorders which monitor non-periodic occurrences either require a large data storage capacity or are required to transmit the data to a remote site for recording. A blood pressure monitor for ambulatory patients invented by V. David Squires et al (U.S. Pat. No. 4,216,776) records data on a continuously-running portable tape recorder. This method can only record continuous data for a limited amount of time and might, because of its potential size, inhibit the normal movement of an ambulatory patient. U.S. Pat. No. 4,326,535 to Charles H. Steffel et al entitled "Circuit and Method for the Radio Telemetry of Esophageal pH in an ECG Radio Telemetry System" overcomes the data storage problem by transmitting pH values from the patient's unit to a remote site for recording. Although, the patient's unit can be reduced in size, the patient's activity is limited to the transmitter range. Accordingly, the range of patient activity in which pH levels can be monitored is limited.